The present invention relates to adjustable beds for the healthcare and home markets and, more particularly, to an adjustable bed including a mechanical jack and linkage for raising and lowering a mattress frame with respect to a base frame.
A wide variety of adjustable, multi-position beds are presently available. Such beds may be used in hospitals, nursing homes, extended care facilities and also in the home. A typical adjustable bed includes a mattress frame divided into a plurality of sections. The frame may include a head section, a seat section and a leg or foot section. The sections are positionable so that the patient or user may be moved from a flat, resting position to a raised, seated position. Typically, the sections are positioned by a motor drive, by hand operated cranks or by the user's weight.
A high/low mechanism may be included to raise the mattress frame from a lowered, rest position to a raised position for easier access to the patient by nursing or hospital personnel. A typical high/low mechanism includes a parallelogram or "X" linkage and a jack. Examples of prior adjustable beds may be found in commonly owned U.S. Pat. No. 5,105,486 entitled ADJUSTABLE BED, which issued on Apr. 21, 1992 to Peterson; U.S. Pat. No. 4,231,124 entitled HOSPITAL BEDS, which issued on Nov. 4, 1980 to Croxton and U.S. Pat. No. 3,733,623 entitled HOSPITAL BEDS, which issued on May 22, 1973 to Croxton.
Prior jacks incorporated in adjustable bed high/low mechanisms have used hydraulic piston cylinders and screw drives. In addition, mechanical jacks have been proposed which use a pair of camming or lock plates. One plate acts as a drive plate and the second plate acts as a hold plate. In the aforementioned U.S. Pat. No. 3,733,623, a hospital bed is disclosed including a mechanical jack having an enclosure or housing and a ram extending therefrom. The ram is extended by a drive plate which is moved into locking or wedged engagement with the shaft upon rotation of an actuator shaft. A hold plate is moved out of locking engagement with the ram to permit lowering of the mattress frame by rotation of a second actuator rod or shaft. A pair of raise and lower pedals, a sleeve, a lever and a cam member are provided to alternately rotate the drive shaft and the release shaft.
Prior hydraulic mechanisms have been relatively expensive when compared to the mechanical systems. Hydraulic systems are prone to leakage which causes the mattress frame to lower or sink. In addition, hydraulic systems are position sensitive. Prior mechanical systems have suffered from excessive complexity, excessive size, lack of load capacity and manufacturing difficulties. A need exists for a bed and a jack which is compact, relatively inexpensive, has sufficient load capacity and which is easily manufactured.